Impermeability to liquids and gases.cork owes this feature to the increased presence of suberin. The content by weight is from 39 to 45% of the mass of the cork. This substance has a waterproofing structure, also causing strengthening and heat insulation.
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The cork oak is the world's only cork oak species producing such thick bark of uniform structure, which spontaneously grows as covering over dying tissue. The bark of this tree - in everyday language, "cork" – is a constantly necrotic tissue formed during the life cycle of these trees by the continually expanding cross-section of their trunks and branches. It is visible under a microscope that this tissue is made up of closed dead micro-cells with the appearance of fourteen-sided polyhedra; the intercellular spaces are completely filled with a gaseous mixture almost identical to the air environment surrounding the tree. In 1cm3 of this tissue there are more than 40 million such fourteen-sided cells. Their chemical composition includes: suberin (45%), lignin (27%), cellulose and polysaccharides (12%), tannic acid (6%), wax (5%) and other substances (5%).
Lightness. The air enclosed in the cork micro-cells makes up 90% of its volume and about 50% of the weight, which makes its specific gravity in the range of 190 to 250 kg/m3. It is therefore a material five times lighter than water, and since it does not absorb water, it is virtually unsinkable.
Impermeability to liquids and gases. Cork owes this feature to the increased presence of suberin. The content by weight is from 39 to 45% of the mass of the cork. This substance has a waterproofing structure, also causing strengthening and heat insulation.